Methods of cracking structures and apparatus for cracking structures



Feb. 25, 1969 A. WATSON 3,430,021

METHODS OF CRACKING STRUCTURES AND APPARATUS FOR CRACKING STRUCTURES Filed May 2, 1966 United States Patent 3,430,021 METHODS OF CRACKING STRUCTURES AND APPARATUS FOR CRACKING STRUCTURES Alexander Watson, St. Albans, England, assignor to Minister of Public Building and Works in Her Britannic Majestys Government of the United Kingdom of Great Britain and Northern Ireland, London, England Filed May 2, 1966, Ser. No. 547,023 Claims priority, application Great Britain, May 5, 1965,

18,958/ 65 US. Cl. 219--10.55 1 Claim Int. Cl. B28d 1/00; Hb 9/06 ABSTRACT OF THE DISCLOSURE The method of cracking a structure such as concrete, brick or the like by generating microwave energy and passing part of the energy along each of two wave guides thereby forming two narrow beams of energy which emerge from both wave guides through openings each having a width substantially less than that of any part of the wave guides so that the beams are directed at small areas spaced apart on the surface of the structure to cause local heating which then results in cracking the structure.

This invention relates to a method of cracking a structure and an apparatus for performing the method. The method and the apparatus may be used for cracking concrete structures, brick structures and the like with little noise.

According to the invention, there is provided a method of cracking a structure comprising generating microwave energy, passing said energy along a waveguide, forming a narrow beam of the energy by causing it to emerge from the waveguide through an opening having a width substantially less thanthat of any part of the waveguide and directing said beam at a small area of the surface of the structure for sufficient time to cause such local heating of the structure that cracking of the structure results.

The frequency of the energy is preferably at least 200 megacycles per second and it is best for it to be at least 800 megacycles per second. The beam preferably produces a temperature rise of at least 100 C. at a depth of 5 inches from the area to which it is directed, a temperature rise of at least 200 C. at a depth of 3 inches and a temperature rise of at least 400 C. at the surface.

Examples in accordance with the invention are described below with reference to the accompanying diagrammatic drawing, in which:

FIGURE 1 shows a side View of an apparatus for cracking a structure,

FIGURE 2 shows a sectional view of the apparatus, taken as indicated by the lines and arrows marked II-II in FIGURE 1,

FIGURE 3 shows a view of part of the apparatus, taken as indicated by the arrow III in FIGURE 1,

FIGURE 4 shows a plan view of another apparatus for cracking a structure,

FIGURE 5 shows part of a third apparatus for cracking a structure, by a view corresponding to one taken as indicated by the arrow V in FIGURE 1.

FIGURE 1 shows a conventional generator 1 of microwave energy, at, for example, 892 or 2450 or 5,000 to 6,000 megacycles per second with a power of, for example, 5 kilowatts. The generator is coupled, as indicated by the dotted lines, to one end of a rectangular sheet steel waveguide 2 having its narrow sides 3 vertical. The end of the waveguide remote from the generator 1 is cut off at an acute angle of, say, 12 to 15 to the axis of the waveguide so that all the portions of the waveguide constituting the extreme end of the waveguide lie in a plane which is inclined by the same angle to that axis. The opening at that end of the waveguide is partially closed by a steel closure plate 4 having a narrow rectangular hole 5 close to and parallel to one of its longer sides and inclined by an acute angle to the axis of the waveguide. This hole has a width substantially less than that of any part of the waveguide 2 so the microwave energy leaves the waveguide through the hole 5 in a narrow beam. The plate 4 is laid on, or close to, a concrete, brick or like structure to be cracked and the beam is thereby directed at a small area of the surface of the structure and this causes intense heating of a wedge-shaped portion of the structure extending to a substantial depth and cracking of the structure if the beam is powerful enough and is maintained long enough. It is preferable in the case of concrete to make the heating so intense and prolonged that local melting of the concrete takes place. This will require bringing its temperature to about 1300 C. There is a tendency for the structure to crack along a line corresponding in position to the length of the hole 5 and so the plate 4 is placed with its hole 5 extending just above and along the line where the crack is desired to occur.

It has been found to be more simple to cause a structure of concrete, brick or the like to crack along a given line by intense local heating to a substantial depth of two regions spaced apart on the line and for this purpose apparatus as shown in FIGURE 4 can be used. This comprises a generator 1 coupled to one end of a first waveguide 6, the other end of which is coupled to second and third waveguides 7 and 8, each of which receives half of the energy and is cut off at its other end and has a closure plate 4 with a rectangular hole 5 in it as described above.

FIGURE 5 shows an example in which a generator (not shown) is coupled to one end of a waveguide 2 and the walls of the waveguide at the end remote from the generator are turned outwardly to form flanges 9 to which is welded or bolted a closure plate 4 to which is fixed a copper gauze radiation screen 10 which extends outwardly from the hole in the closure plate 4 and inhibits undesired escape of radiation. The closure plate 4 also carries one or more microswitches 11 (two are shown) which, or each of which, is in a control circuit of the generator and, when the closure plate 4 is close to a concrete or other structure, engages that structure and is thereby put in such a state as to permit the generator to function, whereas if the closure plate is not sufficiently close to the structure, for example due to its having been blown away by an explosion due to the in tense heating, the generator is switched off by the microswitch or one of the microswitches. The construction shown in FIGURE 5 can be adopted in an apparatus according to FIGURES 1 to 3 and in one according to FIG- URE 4.

It is preferable to fill the hole 5 with a material that is permeable to microwave energy and is. not substantially heated thereby, for example the material that is sold under the trade name Sindanyo, in order to prevent pieces that are broken from the structure from entering the waveguide.

I claim:

1. A method of cracking a structure comprising generating microwave energy, passing some of the energy along a first waveguide and some more of it along a second waveguide, forming two narrow beams of the energy by causing it to emerge from the first and second waveguides through respective openings each having a width substantially less than that of any part of the Waveguides and directing said two beams at two small areas spaced apart on the surface of the structure for suflicient time to cause such local heating of the structure that cracking of the structure results.

References Cited UNITED STATES PATENTS 3,251,975 5/1966 Hugenholtz 219-1057 7/1966 Connell et al. 21910.55 2/1967 Piischner 219-10.55

U.S. C1.X.R. 

